Time switch



Dec. 28, 1937. w, KEARSLEY 2,103,907

TIME SWITCH Filed May 15, 1937 Inventor: William K. KeaYSley,

Attorney.

Cal

Patented Dec. 28, 1937 UNITED STATES 2,103,907 'rmm swrrcn William K. Kearsley, Schenectady, N. Y., an

signer to General Electric Company, a corporation of New York Application May 15, 1937, Serial No. 142,836

11 Claims.

My invention relates to improvements in time switches and particularly to time switches for timing switching operations of short durations, for example, from a small fraction of a second to several seconds. The switch is alsoarranged so that, when controlling an alternating-current circuit, the switching operation or operations can be timed to occur at a selected point on the altermating-current or voltage wave, for example, at zero current or voltage.

The switch is an improvement over that described in my United States Letters Patent No. 1,740,405, 'December 1'7, 1929, used for timing high-speed X-ray exposures. The present switch extends the range of adjustment so that it can be used not only for accurately timing high speed or very short duration exposures, such, for example, as one one-hundred-and-twentieth (1/120) of a second, but may also be used for timing exposures up to several seconds so as to cover the complete range of ordinary radiog'raphic work. The invention is, of course, not confined to the timing of X-ray exposures but the switch was primarily designed for that purpose and such use will serve by way of example for explaining the invention.

The features of my invention which are believed to be novel and patentable will be pointed out in the claims appended hereto. For a better understanding of my invention, reference is made in the following description to the accompanying drawing showing a perspective view of a preferred embodiment of my invention as arranged for timing the duration of closure of the energizing circuit of X-ray apparatus.

In explaining the'invention. certain definite speeds, gear ratios, time periods, etc., will be referred to for the purpose of illustration and not by way of limitation, it being understood that such values will be selected in accordance with the way in which the switch is intended to be used but that the invention is not limited in these respects.

'Referring to the drawing, l represents an alternating-current source of supply assumed to be sixty cycles, and it represents an X-ray tube which is arranged to be energized from source "I. The cathode heating circuit of the tube is energized through a transformer l2 and manual switch IS. The plate or operating circuit of the tube is energized through the transformer l4 and serially arranged contacts l5, l8, and ll of my improved time switch.

The switch mechanism is driven by a small synchronous motor I! energized from the sixtycycle source In through a manual switch IS. The motor is assumed to be a four-pole motor and will, therefore, have a synchronous speed of 1800 revolutions per minute. The motor drives a gear wheel 20 normally free to rotate on a cam shaft 5 2|. The gear reduction between the motor and gear wheel 20-is assumed to be twenty to one, and gear 20 thus rotates at a speed of 90 revolutions per minute or one and one-half revolutions per second. Gear 20 may be clutched to shaft 2| so as to drive the same when the sliding clutch pin 22 engages one of a number of evenly-spaced holes 23 in the gear wheel. The pin 22 is secured in the side of a grooved plate 24 splined on and slidable on the cam shaft 2| towards and away from gear 20, the pin 22 can move relative to gear in a circular path having a radius equal to the radius of the circle of holes 23. The clutch is normally held in the disengaged position shown by a spring 25 hearing against an operating fork 20 26 which engages the groove in plate 24. A solenoid 21 is provided for pulling the fork 26 and plate 24 towards gear 20 against the action of spring 25 to engage the clutch when the solenoid is energized. The gear 20 contains ten evenly- 25 spaced holes 23 so that the spacing between the holes corresponds to one-tenth revolution of the gear and a time duration of one-fifteenth of a second.

The cam shaft is provided with adjustable cams 28 and 29 for controlling the movement of contact fingers l5 and I1 towards and away from stationary contact It. The contact fingers l5 and I1 are mounted on insulating supports pivoted at 30. These supports have roller cam followers II, which bear against and are biased towards the cams by springs 32. When the low part of the cams 28 or 201s opposite the corresponding roller 3|, the corresponding contact finger l! or n is permitted to contact with stationary contact It. It will be evident that, by properly ad justing the cams 28 and 29, both fingers l5 and I1 may rest on contact It for anydesired fraction of a revolution of the cam shaft to momentarily close the operating circuit of the X-ray tube. The shaft 2|, when it rotates, is represented to rotate counterclockwise and, with the cams ad justed as shown, contact II will close first, then contact I! will close, next contact ll will open,

and then contact I5 will open. By this serial arrangement ofcontacts, I can obtain a very short duration of closure of the circuit without resorting to a mechanically impracticable rapid movement of the contacts. The contacts I! and I1 individually open and close relatively slowly and their movements in this respect are constant but the duration of circuit closure, i. e., the time during which both contacts l5 and IT engage contact bar 46, may be very short and may be readily adjusted byrotatively adjusting one or both cams on the cam shaft.

As explained above, one-fifteenth of a second corresponds to the time spacing of the holes in gear 20. One-fifteenth of a second corresponds to a whole number of cycles of the alternatingcurrent source of sixty cycles. Thus, there are four complete cycles every one-fifteenth of a second during which the alternating-current and voltage waves pass through zero values eight times. Consequently, if the cams, which are mechanically tied'to the synchronous motor rotor when the clutch is engaged, are set so that the circuit controlled is opened or closed or both opened and closed when the current or voltage wave passes through a zero value or at any other selected point of such wave, such adjustment will hold regardless of which hole 23 of gear 20 pin 22 engages, because the time spacing of these holes corresponds to a whole number of current cycles. Thus, if this feature is used, the time spacing of the holes in gear 26 should correspond to some whole number of cycles or half cycles.

For adjustment of the cams to open the circuit at zero current value, for instance, we may load the circuit controlled until considerable current is flowing therein and then, operating the cams with the synchronous motor, adjust cam 29, which is the opening cam, until a minimum of arcing occurs between contacts l6 and IT. This condition will occur at or very near the zero point of the current wave. Then, having made this adjustment, We may adjust, the closing cam 28 to obtain the desired duration of switch closure. A graduated scale, such as is shown at 32' on the end surface of this cam, may be used for convenience in such adjustment. The correct position of closing cam 29 for operation at any desired point of the alternating-current or voltage wave can also be obtained with the use of an oscillograph.

It will now be evident that, by adjusting cam 28 with respect to cam 29, the duration of circuit closure per complete revolution of cam shaft 2| may be varied from zero up to the time of a half revolution of shaft 2! which, inthe example given, is one-third of a second. Following a switching operation, it is usually desirable that the cam shaft shall automatically come to a stop with the circuit open. Also, it is desirable to obtain circuit-closing operation up to several seconds duration. The manner in which these functions are accomplished automatically but under the control of the operator will now be explained.

I provide a third cam 33 on cam shaft 2| which controls two pairs of contacts 34 and 35 asso' ciated with the circuit of the clutch solenoid 21.

Contacts 34 are provided to assist in the control of the circuit of clutch solenoid 27 when the switch contacts IS, IS, ll are open, and contacts 35 are provided to assist in the control of the circuit of clutch solenoid 2? when switch contacts l5, i6, H are closed. Cam 33 is properly adjusted with respect to cams 28 and 29 to accomplish this result. Thus the cam operated contacts 33 and 35 determine the stopping positions of shaft 2i and cams 28 and 29. Contacts 35 are in series with a pair of on switch contacts 35 and a manual switch contact 38, and contacts 35 are in series with, a pair of off switch contacts 37 and a manual switch contact 39 in parallel with contacts 31. The manual single-pole double-throw switch lever 40, which cooperates with the stationary contacts 38 and 39 in alternate positions, is under the control of the operator and is preferably a switch which he operates with his foot and which, when released, moves to the position shown against contact 39.

The on and off contacts 35 and 31 are actuated by an exposure timing device driven from the synchronous motor l8 through a reducing gear train comprising gears ll to 45, inclusive. This gear train includes a clutch. The clutch is shown at 66. A spring 41 biases the clutch to the open position shown. A lever 48 operated by a solenoid 39 is provided to engage the clutch when the solenoid is energized. This is done when the foot switch 40 is closed on contact 38. This gear train when in operation drives an arm 50,. which starts from a zero position, against a stop 5! as shown and moves in a clockwise direction past the on contacts 36 until it reaches the ofi contacts 31. The on contacts 36 are fixed near the zero position of the arm 50, but the OE contacts 31 are adjustable about the arc of travel of arm 50 in accordance with the timing period desired, which is indicated on a scale 5|. The 01? contacts 31 are carried on an insulating arm 52 pivoted on the axis of rotation of arm 50. The arm 52- carries a pointer 53 indicating on the time scale 5|. As arm 50 moves past the on and oif contacts, a pin 56 thereon momentarily closes these contacts when adjacent thereto. This pin 541 moves the inner contact of pair 36 outward and moves the outer contact of pair 37 inward in closing the contacts. Thus, contacts 3? may be set as close to contacts 36 as desired without interference. When the arm 50 is driven forward by the synchronous motor through the gear train described, a spiral spring 55 secured between a stationary post 56 and the shaft of gear 43 is wound up and, when the clutch 46 is disengaged as above described, spring 55 returns arm 50 to the zero position shown. The parallel branch circuits of solenoid 27 and the circuit of solenoid 59 are conveniently energized from source l0 although this is not essential.

For convenience in calibrating scale 5!, it will be assumed that cam 28 is adjusted with respect to cam 29 to close the operating circuit of the X-ray tube for one-tenth of the period of rotation of gear 20 when cam shaft 2! is continuously driven through a complete revolution; In the example mentioned previously, this period of time .would be one-fifteenth of a second and corresponds to the time required for pin 22 to move from one hole in gear 20 to the next hole, assum ing solenoid 21 is deenergized. Such timing adjustment of cams 28 and 29 may then be considered to be the unit timing period of the device, and scale 5i may be graduated in such time units sothat, when pointer 53 is placed opposite the first small graduation mark 51 above Zero at the lower end of the scale, the device is adjusted for a period of one timing unit or onefifteenth of a second. If placed adjacent the next small graduation mark, the device is adjusted for a period of two timing units or twofifteenths of. a second, etc. For such graduation of scale 55, it will appear that the gear .ratio between the synchronous motor and arm 50 will be such that the arm moves from one such unit graduation to the next while gear 20 is making one-tenth of a revolution.

The operation of my device as thus adjusted and calibrated is as follows:

The parts and circuits are shown in the idle position. The operator, in'preparing to take an X-ray exposure, closes switch |3 to get his X-ra} tube warmed up. He then closes switch l3, starting the synchronous motor, and adjusts pointer 53 to the time exposure position desired. Let us as-- sume that he desires to take an exposure of onefifteenth second. He, therefore, places the pointer 53 opposite the first small graduation mark 51 beyond the zero mark and thus brings the oif contacts 31 very close to the on contacts 33 in the path of actuator 54 of arm 50. The on contact is set opposite the zero mark. The exposure is now taken, the operator stepping on switch 40 and closing it against contact 33. This energizes solenoid 49, clutch 46 is engaged and arm 50 starts to move in a clockwise directioh away from post 5|. It soon reaches the on contacts and closes them momentarily in moving past this position. This .energizes solenoid 21 through contacts 34 and 35. Clutch plate 24 is drawn towards rotating gear 22 and the pin 22 enters the first hole therein which registers therewith, and the cam shaft 2| is started into rotation in a counterclockwise direction. Contact |1 moves against contact bar l6 and then contact bar |5 moves against'the same bar, closing the X-ray energizing circuit. In the meantime, cam 33 has rotated a half revolution and opened the circuit of solenoid 21 at contacts 34 at the same time closing contacts 35. arm 50 has moved to close the off contacts 31 so that the solenoid 21 remains energized continuously until cam shaft 2| has made a complete revolution, by which time the on contacts 36 have opened, solenoid 21 is deenergized, and cam shaft 2| stops in the position shown, contact bars l1 and I having moved away from bar IE to open the X-ray power circuit at the proper time. -The operator now removes his foot from switch 40, solenoid 49 is deenergized, clutch 46 is disengaged, and spring 55 returns arm 50 to the zero position.

Let us now assume that pointer 53 is set opposite the next small graduation beyond graduation mark 51 to obtain a two-fifteenth of a second exposure. Switch 4|) is then closed on contact 38, solenoid 49 is energized, arm 50 moves past and closes the on contacts-36 energizing solenoid 21, pin 22 engages an opening in gear 2|) and cam shaft 2| starts to rotate, making about a half revolution until the X-ray circuit is closed through contact bar l6, contacts 34 are opened, and contacts 35 closed. At this point in the operation, post 54 on arm 50 has not yet closed the 011" contacts 31, consequently, solenoid 21 is deenergized as soon as contacts 34 are opened and cam shaft 2| stops with the X-ray power circuit closed through contacts l5, l8, and 81. Within one-fifteenth of a second, however, post 54 closes off contacts 31 and energizes solenoid 21 through contacts 35 in time to engage pin 22 in the next opening in gear 20. Cam shaft 22 then completes the remaining half of its revolvetion to the stopping position shown. Since contacts 34 are now open, solenoid 21 is deenergized and cam shaft 2| stops with the X-ray circuit open. The operator then removes his foot from switch 40, clutch 46 is disengaged, and arm 50 returns to the zero starting position.

In the operation just described, it is seen that, while the Xray circuit was closed, cam shaft 2| was stopped long enough for pin 22 to skip one hole in gear 20 to the next and the opening of the X-ray circuit was delayed by one time unit period and was thus closed a total of two time unit periods of two-fifteenths of a second.

Now, if a one-second exposure is desired, pointer 53 is set up scale 5| of the small graduations to the longer one-second graduation. In this case, the operation will be similar to that described except that, when the X-ray circuit is closed, pin 22 will be withdrawn from a hole in gear 20 long enough to skip fifteen openings or fifteen time unit periods each of one-fifteenth of a second duration.

It is thus seen that exactly-timed exposures from one-fifteenth of a second up to several seconds may be obtained in steps differing by as little as one-fifteenth of a second, if desired. For example, a timed exposure of five and five-fifteenths seconds may be made with the same absolute accuracy as an exposure of one-fifteenth of a second. The time range of the apparatus will depend on the gear ratio between gear 20 and arm 50. It is practicable to have a time scale on dial 5| up to 20 seconds where the unit time period is one-fifteenth of a second. Such apparatus thus provides a convenient and accurate time switch for the entire range of usual X-ray exposure practice.

It will be noted that the foot switch 40 has a back contact 39 which, when closed, performs the same function as the off contacts 31. This is a convenience and also a safety feature since, if at any time during a lengthy exposure the operator desires to stop the exposure, he merelylifts his foot from switch 40. This energizes solenoid 21 through contacts 35, contact 39, and switch 40 to return the cam shaft 2| to the off position with the X-ray power circuit open.

In accordance with the provisions of the patent statutes, I have described the principle of operation of my invention together with the apparatus which I now consider to represent the best embodiment thereof but I desire to have it understood that the apparatus shown is only illustrative and that the invention may be carried out by other means. 4

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. A time switch comprising, aconstant-speed motor, a cam shaft, a clutch for connecting and disconnecting said shaft to and from driving relation with the motor, a switch, cam means on said shaft for closing said switch during only a selected part of each revolution of said shaft, a solenoid for connecting said clutch, means for disconnecting the clutch when the solenoid is deenergized, an energizing circuit for said solenoid having two parallel branches, each branch containing two sets of control contacts in series relation, a cam on said shaft for operating one set of control contacts of each branch so that one set is closed when the other is open and vice versa, said cam being positioned with respect to the first mentioned cam means to open one set of contacts operated thereby when said switch is open and to open the other set of contacts operateci thereby when said switch is closed, the other sets of control contacts in the parallel branches being normally open, and timing means for momentarily closing one of the normally open contacts and closing the other normally open contacts a selected time period thereafter.

2. A time switch comprising, a constant-speed motor, a shaft, clutch means between said motor and shaft whereby the shaft may be connected in and disconnected from driving relation Cal with said motor, a normally open switch, cam means operated by said shaft for closing said switch during a selected part of each revolution of said shaft, and means for operating said clutch and clutch control means for starting and stopping the rotation of said shaft in a position where the switch is closed and in a position where the switch is open including timing means driven by said motor independently of said shaft for selectively controlling said clutch-operating means, to stop the rotation of said shaft when said switch is closed for a predetermined period of time.

3. A time switch comprising, a constant-speed motor, a shaft, a clutch between said motor and shaft whereby the shaft may be connected in and disconnected from driving relation with said motor, a normally open switch, cam means operated by said shaft for closing said switch during a selected adjustable portion of each revolution of said shaft, means for operating said clutch for starting and stopping rotation of said shaft in positions where said switch is closed and where said switch is open, said clutch-operating means including means driven by said shaft for determining its stopping positions, and timing means driven by said motor independently of said shaft for delaying starting the rotation of said shaft when the switch is closed for a predetermined adjustable period.

4. A time switch comprising, a synchronous motor, a shaft, a clutch between said motor and shaft whereby the shaft may be connected in and disconnected from driving relation with said motor, a normally open switch, cam means operated by said shaft for closing said switch during a-selected adjustable portion of each revolution of said shaft, means for controlling said clutch for starting and stopping said shaft in rotative positions where the switch is closed and where the switch is open, said means including clutch control means driven by said shaft for determining its stopping positions, and timing means driven by said motor independently of said shaft for determining when the shaft shall be started into rotation from either position.

5. A time switch comprising, a synchronous motor, an alternating-current supply therefor, a shaft, a clutch between said motor and shaft whereby the shaft may be connected in and disconnected from driving relation with said motor, a normally open switch, cam means operated by saidshaft for closing said switch during a selected adjustable portion of each revolution of said shaft, means for controlling said clutch for starting and stopping said shaft in rotative positions where the switch is closed and where the switch is open, said means including clutch control means driven by said shaft for determining its stopping positions, and timing means driven by said motor independently of said shaft for determining when the shaft shall be started into rotation from either position, the driving rela tion between said synchronous motor and shaft being such that the closing and opening of said switch can be timed to occur at a selected point of the wave of the alternating current supplied to said motor.

6. A time switch comprising, a synchronous motor, an alternating-current source of supply therefor, a shaft, a clutch having one part in driving relation with said motor and another part in driving relation with said shaft, a no!- mally open switch, cam means operated by said shaftfor closing said switch during a selected positions of the two parts of said clutch, which positions are rotatively spaced from each other by an amount corresponding to the distance the motor-driven part of said clutch is rotated by said synchronous motor during a whole number of half cycles of the alternating-current supplied to said motor.

7. In a time switch, a synchronous motor, a source of alternating-current supply therefor, a shaft, a switch, cam means rotated by said shaft for opening and closing said switch at selected adjustable rotative positions of each revolution of said shaft, and a clutch between said shaft and synchronous motor having one part rotated by said synchronous motor and another part in driving relation with said shaft, one of said parts comprising a disk with evenly-spaced holes therein arranged in a circle and the other part comprising a pin adapted to engage in any one of said holes, the time spacing of said holes with respect to the speed of rotation of the clutch by the synchronous motor corresponding to a whole number of half cycles of the alternating current supplied to said synchronous motor, whereby the switch may be adjusted to open at a predetermined point of the alternating-current wave supplied to said motor irrespective of which hole said pin is engaged in when said clutch is engaged.

8. A time switch comprising a synchronous motor, a shaft, a clutch between said motor and shaft, a switch, cam means driven by said shaft when said clutch is engaged for opening and closing said switch once during each revolution of said shaft, a solenoid which, when energized, engages said clutch, two energizing circuits for said clutch solenoid, both circuits containingcontact means operated in response to the rotation of said shaft for alternately opening and closing their respective circuits when said switch is opened and closed, respectively, and both circuits containing other normally open contact means, electrically-controlled timing means driven independently of said shaft for momentarily closing said normally open contact means one after the other a predetermined selected time interval apart whereby, when the first normally open contact means is closed, the shaft is rotated from switch-openihg to switcheclosing position and then stopped and whereby, when the second normally open contact means is closed, the shaft is rotated from switch-closing to switch-opening position and then stopped, and a ma dually-controlled switch in said clutch solenoid circuit.

A time switch comprising, a Synchronous r-uotor, a cam shaft, a timer, a timer shaft, electrically-operated clutches between said synchronous motor and said shafts, a switch which is closed and opened by each rotation of said cam shaft, a pair of contact means operated by said cam. shaft and controlling its clutch for detercam Shaft for starting the latter-into rotation from its stopping positions, one of said positions being a switch-closing position and the other a switch-opening position, the contact means operated by said timer shaft being adjustable for the purpose of interrupting the rotary movement of said cam shaft in the switch-closing position for different adjustable time periods, a manual switch through which both electrically-operated clutches are energized, and spring means wound by the timer shaft when its clutch is energized for returning the timer to an initial position when its clutch is deenergized.

10. A time switch comprising, a synchronous motor, a cam shaft, an electrically-operated clutch between said motor and cam shaft, 9. switch closed by said cam shaft when in one rotary position and opened when said cam shaft is in another rotary position, a contact timer, a second electrically-operated clutch through which said timer may be operated by said synchronous motor, a plurality of contacts in series-parallel relation in the energizing circuit of the cam ,shaft clutch operated by rotation of said cam shaft and by said timer for automatically controlling the operation of the cam shaft clutch, the contacts controlled by said timer being adjustable for determining the period of closure of said switch, a manual switch in the energizing circuit of both of said clutches which, when closed, starts the timer into operation and permits energization of the cam shaft clutch through the automatically-controlled contacts, said manual switch being biased to an ad position whereby it moves automatically to such position when released, and an auxiliary contact established by such ofi position of the manual switch in the energizing circuit of the cam shaft clutch which assures that the switch operated by the cam shaft will be inmiediately opened in case it is closed when said manual switch is released.

11. A time switch comprising, a synchronous motor, a cam shaft, a switch having movable contact members operated in response to the rotation of said shaft to close the switch for a predetermined fraction of a second during each revolution of said shaft, a clutch between said motor and shaft, means controlled by said shaft for causing the opening of the clutch to stop the rotation of the shaft in positions where the switch is open and where the switch is closed, a timer mechanism operated by said synchronous motor, means controlled bysaid timer mechanlsm for closing the clutch when said shaft is in switch-opening position whereby the shaft is rotated to switch-closing position, and means controlled by said timer mechanism for closing the clutch when said shaft is in switch-closing position whereby the shaft is rotated to switch-opening position, said timer mechanism being adjustable to control said two clutch-closing control means in succession at spaced time intervals apart in time steps equal to said predetermined fraction of a second, whereby said switch shall be closed for any desired number of such fractions of a second.

WIILIAM K. KEARSLEY. 

